These aren't exactly things that usually fit into a phrasebook (at least, as far as I know), so if this would be better elsewhere or as a singular thread about phrasal expressions ...I'm not too sure if the grammar is correct and I have taken a few liberties on how things are put together at times, but since they are supposed to be idioms, proverbs, sayings whatever, I thought that a bit of liberty would be normal. I've put what it is supposed to translate to in [] and included a translation (and some bits of other thoughts).

din'waadar beskar bah manda'yaim [lit. to sell beskar to Mandalore] - to do something useless, to do something redundant; the Mandalorian equivalent to 'carry owls to Athens' [or 'carry coals to Newcastle'] and similar expressions

besbe'tracye bat shebs (besbe'tra'ba'shebs) [lit. weapons on [the] ass] - an expression of disbelief, reluctance, aversion and disagreement – used similiary to 'like hell (I'll do that)', but can be attached to almost any statement; it is, as a word, kind of unwieldy, but could be contracted and used as a heartfelt curse to vent some frustration); from the German expression literally meaning 'the sledge hangs on the ass'

shebs bat tracyn (sheb'a'tracyn) [lit. ass on fire] - if used as a verb it means to spur sb. to action, to make sb. hurry up; as an adjective it describes someone in a great hurry; an alternative might besheb'ettyc [lit. burning ass], but I'm not too clear on the usage of hettyc for that

ne'cuyi Mandal ures gotabe [lit. there is no Mandal without Motors] - sth that cannot be viewed separately; an action that must be followed by another action or it won't be complete (a job half-done), you have to finish what you start; from the German expression literally meaning 'Who says A has to say B, too'

nu'kovid taabe'shya [lit. no head, more feet] - describing a forgetfulness – used in a mildly teasing manner, usually when an errand is run and part is forgotten; this is always without consequence except for a loss of time; from 'Those who can't use their head must use their back'; the second part can be simply implied by the first part if it is intoned as a tease

digur kovid meh nu'tomyc [lit. forget [the] head if [it were] not joint] - describing forgetfulness – used in a slightly condescening manner without actually being considered insulting, used when someone is constantly forgetting vital parts of a task or errand; from the German literally meaning 'to lose/forget one's head if it weren't attached [to the body]; the second part can by implied by the first part

ke'gycir jetii rejorhaa'ir akaan [lit. to order Jedi to declare war] - to have the wrong person for a job, to task someone without the proper qualifications with an important mission; ke'gycir is derived from ke'gyce to simply mean 'to order', and rejorhaa'ir akaan is my quick derivation for 'to declare war'

narir striili'bora [lit. to do a strill's job] and narir shab'ora [lit. do a screwp-up job] - two parts of a whole, the first means doing a good (support) job, while the second means the complete opposite, doing a disservice (especially if done by someone who is supposed to be a professional)